This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Hemorrhage resulting from traumatic injuries is the leading cause of preventable mortality in both the civilian and military settings. The early recognition and monitoring of blood loss would reduce the mortality rate from trauma injuries. We developed a Broadband Diffuse Optical Spectroscopy (DOS) prototype system that combines multi-frequency domain photon migration (FDPM) with time-independent near infrared (NIR) spectroscopy to accurately measure bulk tissue absorption and scattering spectra between 650 and 1000 nm. In this study, the feasibility of DOS to optically monitor progressive reduction in central blood volume in healthy human subjects was assessed by simultaneously quantifying oxy-, deoxy-, and total hemoglobin concentrations and tissue oxygen saturation. LBNP provides an effective platform to study physiological responses and mechanisms associated with acute hemorrhage in humans without confounding variables. Broadband DOS enables quantitative non-invasive monitoring of blood delivery and changes in oxygen delivery to specific sites during incremental hemorrhage situations and may potentially be used for the early recognition and monitoring of blood loss in both civilian and military settings.